Answer:
x=3
Step-by-step explanation:
we first write both equations:
[tex]3x + 4y = 12 \\ 9x - 4y = 24[/tex]
then we add the Left hand sides from both, and compare to the Right hand sides from both:
[tex]3x + 4y + 9x - 4y = 12 + 24 \\ 3x + 9x = 36 \\ 12x = 36 \\ x = 3[/tex]
